Sleep apnea treatment apparatus

ABSTRACT

Apparatus for delivering pressurized gas to the airway of a patient including: a gas flow generator for providing a flow of gas, a breathing appliance for sealingly communicating with the airway of the patient, and a conduit for delivery of the gas flow to the airway of the patient, the conduit having a first end connected to the gas flow generator and a second end connected to the breathing appliance. The apparatus further includes at least one sensor in fluid communication with the conduit and located substantially at the gas flow generator for detecting conditions corresponding to breathing patterns of the patient and generating signals corresponding to the conditions, and an information processor for receiving the signals and for controlling the output of the gas flow generator responsive to the signals.

FIELD OF THE INVENTION

The present invention relates generally to methodology and apparatus fortreatment of sleep apnea and, more particularly, to mono-level, bi-leveland variable positive airway pressure apparatus.

BACKGROUND OF THE INVENTION

The sleep apnea syndrome afflicts an estimated 1% to 5% of the generalpopulation and is due to episodic upper airway obstruction during sleep.Those afflicted with sleep apnea experience sleep fragmentation andintermittent, complete or nearly complete cessation of ventilationduring sleep with potentially severe degrees of oxyhemoglobindesaturation. These features may be translated clinically into extremedaytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension,congestive heart failure and/or cognitive dysfunction. Other sequelae ofsleep apnea include right ventricular dysfunction with cor pulmonale,carbon dioxide retention during wakefulness as well as during sleep, andcontinuous reduced arterial oxygen tension. Hypersomnolent sleep apneapatients may be at risk for excessive mortality from these factors aswell as by an elevated risk for accidents while driving and/or operatingpotentially dangerous equipment.

Although details of the pathogenesis of upper airway obstruction insleep apnea patients have not been fully defined, it is generallyaccepted that the mechanism includes either anatomic or functionalabnormalities of the upper airway which result in increased air flowresistance. Such abnormalities may include narrowing of the upper airwaydue to suction forces evolved during inspiration, the effect of gravitypulling the tongue back to appose the pharyngeal wall, and/orinsufficient muscle tone in the upper airway dilator muscles. It hasalso been hypothesized that a mechanism responsible for the knownassociation between obesity and sleep apnea is excessive soft tissue inthe anterior and lateral neck which applies sufficient pressure oninternal structures to narrow the airway.

The treatment of sleep apnea has included such surgical interventions asuvulopalatopharyngoplasty, gastric surgery for obesity, andmaxillo-facial reconstruction. Another mode of surgical interventionused in the treatment of sleep apnea is tracheostomy. These treatmentsconstitute major undertakings with considerable risk of postoperativemorbidity if not mortality. Pharmacologic therapy has in general beendisappointing, especially in patients with more than mild sleep apnea.In addition, side effects from the pharmacologic agents that have beenused are frequent. Thus, medical practitioners continue to seeknon-invasive modes of treatment for sleep apnea with high success ratesand high patient compliance including, for example in cases relating toobesity, weight loss through a regimen of exercise and regulated diet.

Recent work in the treatment of sleep apnea has included the use ofcontinuous positive airway pressure (CPAP) to maintain the airway of thepatient in a continuously open state during sleep. For example, U.S.Pat. No. 4,655,213 discloses sleep apnea treatments based on continuouspositive airway pressure applied within the airway of the patient.

An early mono-level CPAP apparatus is disclosed in U.S. Pat. No.5,117,819 wherein the pressure is measured at the outlet of the blowerso as to detect pressure changes caused by the patient's breathing. Thearrangement is such that the control motor is regulated by themicroprocessor to maintain the pressure at constant level regardless ofwhether the patient is inhaling or exhaling.

Also of interest is U.S. Pat. No. 4,773,411 which discloses a method andapparatus for ventilatory treatment characterized as airway pressurerelease ventilation and which provides a substantially constant elevatedairway pressure with periodic short term reductions of the elevatedairway pressure to a pressure magnitude no less than ambient atmosphericpressure.

U.S. Pat. Nos. 5,245,995 5,199,424, and 5,335,654, and published PCTApplication No. WO 88/10108 describes a CPAP apparatus which includes afeedback/diagnostic system for controlling the output pressure of avariable pressure air source whereby output pressure from the air sourceis increased in response to detection of sound indicative of snoring.The apparatus disclosed in these documents further include means forreducing the CPAP level to a minimum level to maintain unobstructedbreathing in the absence of breathing patterns indicative of obstructedbreathing, e.g., snoring.

Bi-level positive airway therapy for treatment of sleep apnea andrelated disorders is taught in U.S. Pat. No. 5,148,802. In bi-leveltherapy, pressure is applied alternately at relatively higher and lowerprescription pressure levels within the airway of the patient so thatthe pressure-induced patent force applied to the patients airway isalternately a larger and a smaller magnitude force. The higher and lowermagnitude positive prescription pressure levels, which will behereinafter referred to by the acronyms IPAP (inspiratory positiveairway pressure) and EPAP (expiratory positive airway pressure), may beinitiated by spontaneous patient respiration, apparatus preprogramming,or both, with the higher magnitude pressure (IPAP) being applied duringinspiration and the lower magnitude pressure (EPAP) being applied duringexpiration. This method of treatment may descriptively be referred to asbi-level therapy. In bi-level therapy, it is EPAP which has the greaterimpact upon patient comfort. Hence, the treating physician must becognizant of maintaining EPAP as low as is reasonably possible tomaintain sufficient pharyngeal patency during expiration, whileoptimizing user tolerance and efficiency of the therapy.

Both inspiratory and expiratory air flow resistances in the airway areelevated during sleep preceding the onset of apnea, although the airwayflow resistance may be less during expiration than during inspiration.Thus it follows that the bi-level therapy as characterized above shouldbe sufficient to maintain pharyngeal patency during expiration eventhough the pressure applied during expiration is generally not as highas that needed to maintain pharyngeal patency during inspiration. Inaddition, some patients may have increased upper airway resistanceprimarily during inspiration with resulting adverse physiologicconsequences. Thus, depending upon a particular patient's breathingrequirements, elevated pressure may be applied only during inhalationthus eliminating the need for global (inhalation and exhalation)increases in airway pressure. The relatively lower pressure appliedduring expiration may in some cases approach or equal ambient pressure.The lower pressure applied in the airway during expiration enhancespatient tolerance by alleviating some of the uncomfortable sensationsnormally associated with mono-level CPAP.

Although mono-level, bi-level and variable positive airway pressuretherapy has been found to be very effective and generally well accepted,they suffer from some of the same limitations, although to a lesserdegree, as do the surgery options; specifically, a significantproportion of sleep apnea patients do not tolerate positive airwaypressure well. Thus, development of other viable non-invasive therapiesand better versions of existing therapies has been a continuingobjective in the art.

In this regard, even the more sophisticated CPAP apparatus heretoforeknown in the art, including those described in U.S. Pat. Nos. 5,245,9955,199,424, and 5,335,654, and published PCT Application No. WO 88/10108,suffer from certain operational disadvantages which stem from thestructural relationships of their essential components.

More particularly, the CPAP apparatus disclosed in U.S. Pat. Nos.5,245,995 5,199,424, and 5,335,654, and published PCT Application No. WO88/10108 provide feedback/diagnostic systems including at least onesensor (typically an audio transducer such as a microphone) incommunication with the patient's respiratory system. This sensor islocated on or is connected to means (such as a breathing mask or nasalprongs) in sealed air communication with a patient's respiratory system.The sensor continuously senses the patient's breathing patterns andtransmits signals indicative of those patterns to information processingmeans which control the motor speed of a blower. The breathing patternsignals can also be continuously monitored and/or recorded, therebyimparting to the apparatus a diagnostic as well as therapeuticcapability.

The blower delivers pressurized air to the patient through a length ofconduit and the breathing mask or nasal prongs. When the sensor detectsbreathing patterns indicative of obstructed breathing, e.g., snoring, ittransmit signals corresponding to this condition to the informationprocessing means which causes an increase in blower motor speed and,therefore, blower pressure output, until unobstructed breathing iseliminated. The system also includes logic whereby blower motor speed(and blower pressure output) is gradually decreased if unobstructedbreathing patterns are detected over a preselected period of time. Thepurpose of this feature is to provide the patient with a pressureminimally sufficient to maintain airway patency during unobstructedbreathing, thereby enhancing patient comfort and therapy compliance.

Despite the general effectiveness of these apparatus, however, thestructural relationship of their feedback/diagnostic system with respectto the patient's breathing circuit (i.e., the blower, gas deliveryconduit, and breathing mask or nasal prongs) results in an arrangementof lesser reliability than would otherwise be desirable.

For example, certain feedback/diagnostic systems utilize a breathingpattern sensor mounted on or connected to the breathing mask or nasalprongs. Such an arrangement requires a length of feedback conduit to beadded to the patient's breathing circuit. The feedback conduit extendsfrom the breathing patterns sensor at the mask to the blower.

Such an added feedback conduit renders the patient's breathing circuitcumbersome and increases the risk of entanglement of the feedbackcircuit. The arrangement also increases the risk of the feedback conduitbecoming kinked or having the conduit accidently disconnected from thebreathing mask, either of which render the device inoperable. Such afeedback conduit also requires frequent cleaning because it is incontact with the patient's expired air.

An advantage exists, therefore, for an apparatus for deliveringpressurized air to the airway of a patient which includes afeedback/diagnostic system of higher reliability and increased ease ofuse, whereby diagnostic accuracy and patient comfort and adherence tothe therapy administered by the apparatus are optimized.

SUMMARY OF THE INVENTION

The present invention contemplates a novel and improved method fortreatment of sleep apnea as well as novel methodology and apparatus forcarrying out such improved treatment method. The invention contemplatesthe treatment of sleep apnea through application of pressure at variancewith ambient atmospheric pressure within the upper airway of the patientin a manner to promote patency of the airway to thereby relieve upperairway occlusion during sleep.

According to the invention, positive pressure may be applied at asubstantially constant, "mono-level," patient-specific prescriptionpressure, at alternatively higher (IPAP) and lower (EPAP) "bi-level"pressures, or at variable pressures within the airway of the patient tomaintain the requisite patent or "splint" force to sustain respirationduring sleep periods.

In all embodiments considered to be within the scope of the instantinvention, the apparatus for delivering pressurized breathing gas to theairway of a patient comprises a breathing gas flow generator,information processing means for controlling the output of the gas flowgenerator, and a length of flexible conduit connected at one end to thegas flow generator and at an opposite end to a patient interface meanssuch as a breathing mask or nasal prongs. By controlling the output ofthe gas flow generator, the information processing means likewisecontrols the pressure of the breathing gas delivered to the patientthrough the flexible conduit and the patient interface means.

The apparatus further includes a novel feedback system which may impartboth therapeutic as well as diagnostic capability to the apparatus. Thefeedback system includes at least one sensor means, such as a pressureor flow responsive transducer, located on, within or closely adjacent tothe gas flow generator. The sensor means continuously senses thepatient's breathing patterns and transmits signals indicative of thosepatterns to the information processing means. The apparatus may alsoinclude means whereby these signals can also be continuously monitoredand/or recorded whereby the patient's specific breathing disorder may bediagnosed as well as treated by the apparatus.

Like the feedback/diagnostic systems known in the art, when the sensordetects breathing patterns indicative of obstructed breathing, ittransmits signals corresponding to this condition to the informationprocessing means. This means, which may be any suitable microprocessoror central processing unit (CPU), then causes the flow generator toincrease its output which increases the air pressure delivered to thepatient until obstructed breathing is no longer detected. The systemalso includes logic whereby the flow generator output is graduallydecreased if unobstructed breathing patterns are detected over apreselected period of time. This feature serves to provide the patientwith a pressure minimally sufficient to maintain airway patency duringunobstructed breathing, thus enhancing patient comfort and therapycompliance.

Unlike other positive airway pressure apparatus equipped withfeedback/diagnostic systems including a breathing patterns sensorlocated on or connected to the patient interface, the apparatusaccording to the present invention finds its breathing patterns sensorsituated generally at the end of the breathing circuit remote from thepatient. That is, the sensor is preferably located within, on or isconnected closely adjacent to the outlet of the gas flow generatorcontroller. Situating the breathing patterns sensor at this region ofthe breathing circuit realizes considerable improvements in apparatusperformance characteristics and in particular sensor reliability andease of use.

More specifically, by distancing the breathing patterns sensor from thepatient interface (i.e., the breathing mask or nasal prongs), thatportion of the along the patient's breathing circuit is eliminated, andonly a relatively shorter feedback conduit is required and is provided.Consequently, the patient's breathing circuit is rendered considerablyless cumbersome, the risk of entanglement is negatived, and anyannoyance of the patient is minimized. The length of the shorterfeedback conduit reduces, if not totally eliminates, the risk of beingkinked or accidently disconnected from the patient's breathing circuit.Additionally, frequent cleaning of the shorter feedback conduit is notrequired because it is not in direct contact with the patient's expiredair. The shorter feedback conduit also reduces the materials cost forthe system.

Admittedly, placement of the breathing patterns sensor substantially ator near the gas flow generator reduces the responsiveness of theapparatus to the patient's continually changing respiratory needs.However the reduction in responsiveness of the breathing patterns sensoris compensated for by resonant tuning of the system. That is, thefrequency response of the patient's breathing circuit and internaltubing of the present system is acoustically tuned to optimally transmitsounds with frequency content which is known to be indicative of upperairway obstructions. Thus the tuned resonance is such that sounds(snores) with frequencies near the resonant frequency are amplified,thus boosting the signal-to-noise ratio (more accurately the ratio ofsnore noise to gas flow generator noise) back to the level which iscomparable to that which has been obtained by sensing at the patientinterface. As illustration, a patient's lack of demand or a reduceddemand for inspiratory air often precedes, frequently by severalseconds, by the onset of an audible snore or other pronounced physicalmanifestation indicative of obstructed breathing. The breathing patternsensors typically must detect such salient occurrences before theyregister an obstructed breathing event. In such case, the sensor wouldtransmit data to the CPU such that the CPU could step up the output ofthe flow generator well in advance of not only an apneic event but alsoprior to the characteristic audible snore patterns which normallyprecede such an event. Known breathing pattern sensors typicallyaccomplish this while being located on or connected to the patientinterface. The sensor of the present invention, on the other hand, maybe an equally responsive pressure or flow transducer sensitive topressure or flow variations of any selected magnitude and/or frequency,but located within, on or connected closely adjacent to the outlet ofthe gas flow generator.

Other details, objects and advantages of the present invention willbecome apparent as the following description of the presently preferredembodiments and presently preferred methods of practicing the inventionproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily apparent from the followingdescription of preferred embodiments thereof shown, by way of exampleonly, in the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of a prior art CPAP apparatusincluding a patient feedback/diagnostic system;

FIG. 2 is a functional block diagram showing a preferred embodiment ofthe present invention;

FIG. 3 is a functional block diagram of a further preferred embodimentof the present invention; and

FIG. 4 is a view schematically illustrating a preferred embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

There is generally indicated at 10 in FIG. 1, in the form of afunctional block diagram, a mono-level CPAP apparatus including apatient feedback/diagnostic system generally and schematicallyrepresentative of the apparatus disclosed in U.S. Pat. Nos. 5,245,9955,199,424, and 5,335,654, and published PCT Application No. WO 88/10108.

Apparatus 10 includes a blower 12 driven by an electric blower motor 14.The speed of motor 14 and thus the output of the blower 12 is controlledby an information processing means or central processing unit (CPU) 16.The output of the blower is connected by a suitable length of flexiblegas delivery conduit means 18 to a patient interface means 20 such as,for example, nasal prongs or, as illustrated, a breathing mask which isin sealed air communication with the airway of a patient 22. Ifconstructed as a breathing mask the patient interface means 20 mayinclude suitable exhaust port means, schematically indicated at 24, forexhaust of breathing gas during expiration. Exhaust port means 24 may bea conventional non-rebreathing valve or one or more continuously openports which impose a predetermined flow resistance against exhaust gasflow. Apparatus 10 also includes a suitable pressure transducer 26located on or connected to the patient interface means 20. Typically,the pressure transducer 26 is an audio transducer or microphone. When,for example, snoring sounds occur the pressure transducer detects thesounds and feeds corresponding electrical signals to the CPU 16 which,in turn, generates a flow generator motor control signal. Such signalincreases the speed of the flow generator motor, thereby increasingoutput pressure supplied to the patient by the blower 12 through conduitmeans 18 and the patient interface means 20. The system may includesuitable data storage and retrieval means (not illustrated) which may beconnected to CPU 16 to enable medical personnel to monitor and/or recordthe patient's breathing patterns and thereby diagnose the patient'sparticular respiratory disorder and breathing requirements.

As snoring is caused by vibration of the soft palate, it is thereforeindicative of an unstable airway and is a warning signal of theimminence of upper airway occlusion in patients that suffer obstructivesleep apnea. Snoring is itself undesirable not only as it is adisturbance to others but it is strongly believed to be connected withhypertension. If the resultant increase in system output pressure issufficient to completely stabilize the airway, snoring will cease. If afurther snoring sound is detected, the pressure is again incrementallyincreased. This process is repeated until the upper airway is stabilizedand snoring ceases. Hence, the occurrence of obstructive apnea can beeliminated by application of minimum appropriate pressure at the time ofuse.

The feedback circuit also includes means to gradually decrease theoutput pressure if an extended period of snore-free breathing occurs inorder to ensure that the pressure is maintained at a level as low aspracticable to prevent the onset of apnea. This effect can be achieved,for example, by the CPU 16 which, in the absence of an electronic signalfrom the pressure transducer 26 indicative of snoring, continuously andgradually reduces the flow generator speed and output pressure over aperiod of time. If, however, a snore is detected by the first pressuretransducer, the CPU will again act to incrementally increase the outputof the flow generator. The feedback circuit of the present invention aswill be discussed hereinafter in connection with FIG. 2 preferablyincludes similar means.

In use, a patient using apparatus 10 may connect himself to theapparatus and go to sleep. The output pressure is initially at a minimumoperating value of, for example, approximately 3 cm H₂ O gauge pressureso as not to cause the previously mentioned operational problems ofhigher initial pressures. Not until some time after going to sleep, thepatient's body relaxes, will the airway start to become unstable and thepatient begin to snore. The pressure transducer 26 will then respond toa snore, or snore pattern, and via the CPU 16 increase the blower motorspeed such that output pressure increases, for instance, by 1 cm H₂ Ofor each snore detected. The pressure can be increased relativelyrapidly, if the patient's condition so requires, to a working pressureof the order of 8-20 cm, which is a typical requirement. Additionally,for ease of monitoring the variation over time a parameter such aspressure output can be recorded in some convenient retrievable form andmedium (such as the aforesaid data storage and retrieval means) forperiodic study by medical personnel.

If for example in the early stages of sleep some lesser output pressurewill suffice, apparatus 10 will not increase the pressure until needed,that is, unless the airway becomes unstable and snoring commences, noincrease in airway pressure is made. By continuously decreasing theoutput pressure at a rate of, for example, 1 cm H₂ O each 15 minutes inthe absence of snoring, the pressure is never substantially greater thanthat required to prevent apnea.

The feedback circuit of FIG. 1 provides a system which adjusts apparatusoutput pressure according to variations in a patient's breathingrequirements throughout an entire sleep period. Further, apparatus 10will likewise accommodate variable output pressure requirements owing togeneral improvements or deteriorations in a patient's general physicalcondition as may occur over an extended period of time.

Despite the general effectiveness of apparatus 10, however, thestructural relationship of its feedback/diagnostic system with respectto the patient's breathing circuit (i.e., the blower, gas deliveryconduit, and breathing mask) results in an arrangement which can becumbersome to use, inconvenient to maintain, and of lesser reliability.

The present invention overcomes deficiencies of currently availablepositive airway pressure apparatus such as apparatus 10 by proposing anovel feedback/diagnostic system which is adapted for use in mono-level,bi-level and variable output positive airway pressure apparatus.Although for brevity the invention will be described in detail as it maybe adapted to mono-level positive airway pressure apparatus, it isfurther contemplated that the particulars of the present invention mayalso be gainfully adapted to equally preferred embodiments includingbi-level and variable positive airway pressure apparatus, the generalcharacteristics and functions of which are well known in the art.However, the particulars of the "bi-level" and "variable" positiveairway pressure apparatus embodiments of the present invention will notbe described at length. Consequently, it will nevertheless be understoodthat the presently proposed arrangement and operation of thefeedback/diagnostic system components with respect to the breathingcircuit will be substantially the same for a "bi-level" and "variable"positive airway pressure apparatus as those discussed hereinafter inconnection with the "mono-level" embodiment of the invention.

Referring to FIG. 2, there is illustrated in the form of a functionalblock diagram, an apparatus 110 representing perhaps the simplest of thepresently preferred embodiments of the invention contemplated byapplicants. Apparatus 110 includes a gas flow generator 114 (e.g., ablower) which receives breathing gas from any suitable source such as apressurized bottle or the ambient atmosphere.

Located substantially at, i.e., within, on or connected closely adjacentto, the outlet of the gas flow generator 114 is a sensor means 126 influid communication with a flexible gas delivery conduit means 118. Oneend of conduit 118 is connected to the outlet of the gas flow generator114. The conduit 118 communicates the output of the gas flow generator114 to a patient interface means or breathing appliance 120 that isconnected to the opposite end of the conduit 118. The patient interfacemeans 120 may be a mask of any suitable known construction which is wornby patient 122 and is in sealed communication with the patient's airway.The patient interface means 120 may preferably be a nasal mask or a fullface mask as illustrated and hereinafter referred. Other breathingappliances which may be used in lieu of a mask may include nasalcannulae, an endotracheal tube, or any other suitable appliance forinterfacing between a source of breathing gas and a patient.

The mask 120 includes suitable exhaust port means, schematicallyindicated at 124, for exhaust of breathing gases during expiration.Exhaust port means 124 preferably is a continuously open port providedin the mask 120 or a non-rebreathing valve (NRV) situated closelyadjacent the mask in conduit 118. The exhaust port means imposes asuitable flow resistance upon exhaust gas flow to permit an informationprocessing means or central processing unit (CPU) 130, which receivessignals generated by sensor means 126 as indicated at 128, to controlthe output of the gas flow generator in a manner to be described atgreater length hereinafter.

The exhaust port means 124 may be of sufficient cross-sectional flowarea to sustain a continuous exhaust flow of approximately 15 liters perminute. The flow via exhaust port means 124 is one component, andtypically the major component of the overall system leakage, which is animportant parameter of system operation.

Sensor means 126 preferably comprises at least one suitable pressure orflow transducer which continuously detects pressure or flow dischargesubstantially at the outlet of the gas flow generator, which pressure orflow reflects the patient's breathing patterns. Concurrently, the sensormeans 126 generates output signals 128 corresponding to the continuouslydetected gas pressure or flow from the gas flow generator 114 andtransmits these signals to a pressure or flow signal conditioningcircuit of the CPU 130 for derivation of a signal proportional to theinstantaneous pressure or flow rate of breathing gas within conduit 118.Such flow or pressure signal conditioning circuit may for example be ofthe type described in U.S. Pat. No. 5,148,802, the disclosure of whichis incorporated herein by reference.

Depending upon the characteristics of the conditioned flow or pressuresignal, the CPU may generate a command signal 132 to either increase ordecrease the output of the gas flow generator 114, e.g., to increase ordecrease the speed of an electric motor (not illustrated) thereof. Thegas flow generator 114, sensor means 126 and CPU 130 thus comprise afeedback circuit or system capable of continuously and automaticallycontrolling the breathing pressure supplied to the patient's airwayresponsive to the patient's respiratory requirements as dictated by thepatient's breathing patterns.

Like the feedback/diagnostic systems known in the art, when the sensormeans 126 detects breathing patterns indicative of obstructed breathing,it transmits signals corresponding to this condition to the CPU 130. TheCPU then causes the gas flow generator 114 to increase its output whichincreases the air pressure delivered to the patient until obstructedbreathing is no longer detected. The system also includes means such asappropriate logic programmed into the CPU whereby the gas flow generatoroutput is gradually decreased if unobstructed breathing patterns aredetected over a preselected period of time. This feature serves toprovide the patient with a pressure minimally sufficient to maintainairway patency during unobstructed breathing, thus enhancing patientcomfort and therapy compliance.

In many respects, therefore, the feedback circuit of the presentinvention performs similarly to the feedback circuits disclosed inpreviously discussed U.S. Pat. Nos. 5,245,995 and 5,199,424 andpublished PCT Application No. WO 88/10108. However, by situating thesensor means 126 proximate the outlet of the gas flow generator ratherthan proximate the patient interface means 120 many significant benefitsin apparatus performance are realized, which translate into increasedpatient comfort and therapy compliance.

Admittedly, placement of the breathing patterns sensor substantially ator near the gas flow generator reduces the responsiveness of theapparatus to the patient's continually changing respiratory needs.However the reduction in responsiveness of the breathing patterns sensoris compensated for by resonant tuning of the system. That is, thefrequency response of the patient's breathing circuit and internaltubing of the present system is acoustically tuned to optimally transmitsounds with frequency content which is known to be indicative or upperairway obstructions. Thus the tuned resonance is such that sounds withfrequencies near the resonant frequency (snores) are amplified, thusboosting the signal-to-noise ratio (more accurately the ratio of snorenoise to gas flow generator noise) back to the level which is comparableto that which has been obtained by sensing at the patient interface. Asillustration, a patient's lack of demand or a reduced demand forinspiratory air often precedes, frequently by several seconds, the onsetof an audible snore or other pronounced physical manifestationindicative of obstructed breathing. In such case, the sensor means wouldtransmit data to the CPU 130 such that the CPU may step up the output ofthe gas flow generator 114 well in advance of not only an apneic eventbut also prior to the characteristic audible snore patterns whichnormally precede such an event. Known breathing pattern sensorstypically accomplish this while being located on or connected to thepatient interface. The sensor of the present invention, on the otherhand, may be an equally responsive pressure or flow transducer sensitiveto pressure or flow variations of any selected magnitude and/orfrequency, but located within, on or connected closely adjacent to theoutlet of the gas flow generator.

In addition to its accurate and responsive feedback capability, thefeedback circuit of apparatus 110, by virtue of the strategic placementof sensor means 126, also affords medical personnel the opportunity tomonitor and/or record the patient's breathing activity with highprecision. With this capability, the medical personnel may confidentlydiagnose the patient's particular breathing disorder, prescribe theappropriate therapy, and monitor the patient's progress while undergoingtreatment using apparatus 110. In this regard, such monitoring and/orrecording may be achieved by system data storage and retrieval means140.

System data storage and retrieval means 140 may within the scope of thepresent invention comprise any suitable computer memory into whichinformation can be written and from which information can be read.Representative, although not limitative, embodiments of the system datastorage and retrieval means may therefore include a random access memory(RAM), magnetic tapes or magnetic disks which may be incorporated into astand-alone personal computer, mainframe computer, or the like (notillustrated).

System data storage and retrieval means 140 may be configured to recordoutput data from gas flow generator 114 and/or, as indicated, it maycompile data from one or more data input lines 142 which communicatedata transmitted by other sensors or monitors (not shown) which areoperatively connected to other patients in a manner known to thoseskilled in the art.

FIG. 3 reveals, in the form of a functional block diagram, an apparatus210 for use in treatment of sleep apnea and related disorders that isconstructed in accordance with a further preferred embodiment of thepresent invention. For brevity, only those elements of apparatus 210which depart materially in structure and/or function from theircounterpart elements in FIG. 2 will be described in detail where suchdescription is necessary for a proper understanding of the invention. Inother words, except where otherwise indicated, gas flow generator 214,conduit means 218, patient interface means 220, exhaust port means 224,sensor means 226, CPU 230 and system data storage and retrieval means240 of FIG. 3 desirably are constructed as and function substantiallyidentically to gas flow generator 114, conduit 118, patient interfacemeans 120, exhaust port means 124, sensor means 126, CPU 130 and systemdata storage and retrieval means 140 discussed hereinabove in connectionwith FIG. 2.

The primary distinction between apparatus 210 and apparatus 110 is thepresence of a pressure controller 216 which may be controlled separatelyfrom and in addition to the gas flow generator 214 by CPU 230.

The pressure controller 26 is thus operative to regulate, at least inpart, the pressure of breathing gas within the conduit means 218 andthus within the airway of the patient 222. Pressure controller 216 islocated preferably, although not necessarily, within or closelydownstream of flow generator 214 and may take the form of an adjustablevalve, the valve being adjustable to provide a constant or variablepressure drop across the valve for all flow rates and thus any desiredpressure within conduit means 218.

Interposed in line with conduit means 218, downstream and substantiallyadjacent to pressure controller 216, is a suitable sensor means 226 suchas a pressure or flow transducer which generates an output signal thatis fed as indicated at 228 to a pressure or flow signal conditioningcircuit of CPU 230 for derivation of a signal proportional to theinstantaneous pressure or flow rate of breathing gas within conduitmeans 218 to the patient.

Depending upon the instantaneous pressure or flow condition detected bysensor means 226, which feeds a signal 228 corresponding to thatcondition to the CPU 230, the CPU may generate and transmit a commandsignal 232 to increase or decrease the output of the gas flow generator214 in the manner discussed above in connection with the description ofFIG. 2. Alternatively, or in addition to, command signal 232, the CPUmay generate and transmit command signal 234 (shown in dashed line) tothe pressure controller 216 to adjust the pressure drop producedthereby. In this way particularly sophisticated instantaneous pressureoutput patterns may be achieved to satisfy the demands of the patient ona breath-to-breath basis.

Furthermore, data storage and retrieval means 240 may be configured tocompile input not only from the gas flow generator 214 and from thepatient 222 via input lines 242, but also from the pressure controller216 to provide the overseeing medical personnel an even more completerepresentation of the patient's respiratory activity.

FIG. 4 schematically illustrates an arrangement wherein apparatus 310includes a device 312 incorporating the flow generator 314, breathingpatterns sensor means 326, a CPU or central processing unit 330 whichincludes a pressure controller (not illustrated). The flow generator 314presents a bellows 338 terminating in a circuit coupler 344 presentedexternally of the device 312. A patient or first conduit means 318 hasone end connected to the circuit coupler 344 and an opposite endconnected to the patient interface means 320 which includes exhaust portmeans 324.

Unlike other positive airway pressure apparatus equipped withfeedback/diagnostic systems including a breathing patterns sensorlocated on or connected to the patient interface, the apparatus 310according to the present invention finds its breathing patterns sensormeans 326 situated generally at the end of the breathing circuit remotefrom the patient 322. That is, the sensor 326 is preferably locatedwithin, on or is connected closely adjacent to the outlet of the gasflow generator 314. More specifically, the sensor means 326 comprises apressure transducer 346 operably connected to the CPU 330. The sensormeans 326 is in fluid communication with the patient or first conduitmeans 318 by means of sensor or second conduit 347. In accordance withthe present invention, the sensor or second conduit means 347 comprisesa internal conduit portion 348 disposed entirely within the device 312,and an external conduit portion 350 disposed exteriorly of the device312. The sensor or second conduit means 347 has one end connected to thepressure transducer 346 and an opposite end connected to the patient orfirst conduit means 318 through the circuit coupler 344 and thus providesound pressure communication between the pressure transducer 346 and thepatient or first conduit means 318 through the circuit coupler 344. Thearrangement is such that when the transmitted sound wave is close to theresonant frequency of the system, greatly amplified sound pressure willbe transmitted from the mask 320 through the patient or first conduitmeans 318, the circuit coupler 344, and the sensor or second conduitmeans 347 to the pressure transducer 346. That is, the system respondslike a harmonic oscillator with one degree of freedom.

By taking advantage of moving the sensor means 326 back to the device312, the present invention provides system that is acoustically tuned tooptimally transmit sounds in the frequency range of 20 to 120 Hz (thesame range of sounds that are indicative of upper airway obstructions).

In apparatus such as that illustrated in FIG. 4, the volume and entrancecharacteristics of the bellows 338, the blower 314, and the patientcircuit 318 also affect the resonance properties in a complex manner.Therefore the optimum lengths of the internal and external conduitportions 348, 350 are best verified empirically. This is achieved byplacing a sound source at the patient mask 320, sweeping through therange of frequencies of interest, and measuring the output response ofthe pressure transducer 346. The lengths of the internal and externalconduit portions 348, 350 are varied until the desired frequencyresponse is achieved.

In one operative embodiment of the apparatus of FIG. 4, one-eighth inchinner diameter tubing is used as the internal and external conduitportions 348, 350. A length L of 40 inches of the internal and externalconduit portions 348, 350 was found to provide the desired resonantfrequency, w of 70 cycles per second. At that resonant frequency, theapparatus 310 is acoustically tuned to optimally transmit sounds in thetarget frequency range of 20 to 120 Hz--the primary frequency range ofsounds that are indicative of upper airway obstruction. It should beunderstood, however, that the length L of the internal and externalconduits 348, 350 will change with changes in the system elements. Thatis, the particular type of patient circuit 318, blower 314, bellows 338,circuit coupler 344, and pressure transducer 346 used in the system dodetermine the length L of the internal and external conduits 348, 350that is required to produce the desired resonant frequency of 70 cyclesper second. Likewise, it should be understood that the frequencies ofsounds associated with upper airway obstructions are known to fallwithin a range of about 20 to 2,000 Hz. Therefore, other operativeembodiments of the apparatus may be tuned by similar methods to resonantfrequencies other than 70 Hz.

It should also be apparent that by distancing the breathing patternssensor from the patient interface (i.e., the breathing mask or nasalprongs), the patient conduit means 318 is rendered considerably lesscumbersome, the risk of entanglement is negatived, and the annoyance ofthe patient is minimized. The length of the shorter feedback conduitreduces, if not totally eliminates, the risk of being kinked oraccidently disconnected from the patient's breathing circuit.Additionally, frequent cleaning of the shorter feedback conduit is notrequired because it is not in direct contact with the patient's expiredair. The shorter feedback conduit also reduces the materials cost forthe system.

Although the invention has been described in detail for the purpose ofillustration, it is to be understood that such detail is solely for thatpurpose and that variations can be made therein by those skilled in theart without departing from the spirit and scope of the invention exceptas it may be limited by the claims.

What is claimed is:
 1. Apparatus for delivering pressurized gas to theairway of a patient, said apparatus comprising:gas flow generator meansfor providing a flow of said gas; patient interface means for sealinglycommunicating with the airway of a patient; first conduit means fordelivery of said gas flow to the airway of a patient, said first conduitmeans; comprising a first conduit having a first end connected to saidgas flow generator means and a second end connected to said patientinterface means; sensor means in fluid communication with said firstconduit and located substantially at said gas flow generator means fordetecting conditions corresponding to breathing patterns of a patientand generating signals corresponding to said conditions; second conduitmeans for communicating said conditions to said sensor means, saidsecond conduit means comprising a second conduit having one endcommunicating with said sensor means and an opposite end communicatingwith said first conduit and located substantially at said gas flowgenerator means, said second conduit communicating with said firstconduit substantially at said first end of said first conduit, saidsecond conduit being acoustically tuned to optimally transmit soundfrequencies falling within a range which is known to be associated withupper airway obstructions; information processing means for receivingsaid signals and for controlling the output of said gas flow generatormeans responsive to said signals.
 2. The apparatus of claim 1 whereinsaid conditions corresponding to breathing patterns of a patientcomprise the pressure of a gas flow provided by said gas flow generatormeans.
 3. The apparatus of claim 1 wherein said conditions correspondingto breathing patterns of said patient comprise the flow rate of said gasflow provided by said gas flow generator means.
 4. The apparatus ofclaim 1 further comprising a pressure controller connected to said gasflow generator means and said sensor means, said information processingmeans being operably connected to said pressure controller to cause saidpressure controller to regulate the pressure of said gas flow providedby said gas flow generator means responsive to said signals received bysaid sensor means.
 5. The apparatus of claim 1 further comprising meansfor retrieving and storing output data associated with gas flowgenerator means.
 6. The apparatus of claim 4 further comprising meansfor retrieving and storing output data associated with at least one ofsaid gas flow generator means and said pressure controller.
 7. Theapparatus of claim 1 wherein said second conduit includes an internaltubing which optimizes a signal to noise ratio of the detectedconditions to optimally transmit said sound frequencies.